Japanese Patent Application Laid-open Publication (JP-A) No. 2003-160024 discloses a seat belt device configured to enable a passenger to confirm a failure occurring in a pretensioner motor and the like. The disclosed seat belt device includes a motor, a motor driving means, a driving force transmitting means, and a failure determining means. The failure determining means determines the presence or absence of a motor failure on the basis of a current waveform generated when the motor driving means drives the motor while the driving force transmitting means interrupts transmission of a driving force from the motor to a seat belt wind-up device.
In the seat belt device shown in JP 2003-160024 A, detection of a motor failure is started and performed when an ignition switch is turned on, when a driver's-side door switch is turned on, or when depression of a brake pedal is detected. Due to a relatively few motor-failure detection opportunities, it may occur that a passenger cannot be restrained by a seat belt due to a motor failure occurring when an emergency condition happens on the vehicle.
With the foregoing prior problem in view, an object of the present invention is to provide a seat belt device which is capable of appropriately detecting a motor failure.